Electrodynamic loud-speaking apparatus



' Oct. 13,1925.

E. GERLACH ELECTRODYNAMIC LOUD SPEAKING APPARATUS lFim: Jan. 12. 1924 2 Sheets- SheetI 1 Oct. 13,1925.

E. GERLACH ELBG'IRODYNAIIIC LOUD SPEAKING lAPPARATUS rma Jan. 12.11924 2 sheets-sneu 2 Patentea oct. 13, 1925.

nam amaca, or 'smnnlvssrann BERLIN, GERMANY, AssiGNon 'ro SIEMENS & HALSKE, AKTIENGESELLSCHAFT, F SIEMENSSTA'DT, NEAR BERLIN,

GERMANY, A CORPORATION GIGEItMANY.

ELECTRODYNAMIC LoUnsrEaxma Arranaru's.

To all Iwhom it may concern:

Be it known that I, ERWIN. GERLACH, a i y citizen of the German Empire, residing at It has already. ybeen Proposed'tv' design.. electrodynamic lsound responsive `rr`rdevices,

such as microphones or loud-speaking telephones in such a manner, that the diaphragm 15 itself forms the current carrying conductor .and is stretched between the two poles of a. magnet. The diaphragm is set in oscziltions by the influence ofthe magnetic Such devices have, however, such great. disadvanta es, that vtheir practical appli-vv cation ,.was itherto not possible, particular-y ly for the reason that the diaphragm does y not comply with the requirementsmade upon it and that the entire'arrangement leaves much to be desired. i

My invention relates -to an electrodynamic sound responsive device of this 4kind which satisfies all the demands made upon it. -Above all an exceedinglynatural reproduction of the actual sound of the human voice isattained. l v

It is obvious to any o'nekilled-'in the art.

that the devices Ydescribed andshown herein may serve for theconversion of electrical energy into 'sound energy 'as well as for converting sound energy into electrical cnergy without chan ing theconstruction of the device. lIn ot er words, the devices 40 shown may serve as a telephone and a microphone as well, though in the specification in general the device is described as a loud Ispeaker.

The diaphragm,which consists of a -'very fine metal foil, for instancealuminum, is resiliently arranged under light tension in such a manner 'that-it may perform oscillations of large and approximately equal. am litude almost across its entire surface.

' 50 Thls is preferably attained by constructing appuoation med January 12,1924. sei-iai ng. 685,812.

phragm is passed over the rounded edges of adjustable fiat springs. The weight'of the diaphragm is preferably chosen equal to the weight of the volume of air taking part in the oscillations. A suitable confinement of the air chamber can'be effected by means of funnel-shaped sound guides. In order to facilitate the changing of the diaphragm it is suitably disposed on a s cial carrier, preferably of wedge-shape, w iereby a very vconvenient supply. of they electriccurrentVV is ensured.V

In'order to attain very loud reproduction,

it is in some eases, particularlywhen it is desired to save space, advisable employ in# stead of a plurality of diaphragms a sin le one, which is disposed inzigzag between t e poles of the magnet.

If the loud speaker is intended to emanate 4sound in one direction only, the other side of the diaphragm is preferably enclosed 'by a sound-damping, adjustable cavity.

In the accompanying drawingsembodiments of my invention are illustrated diagrammatica-Ally in the form of a' loud speakf er. The drawings represent in:-

- -Fig. 1, a plan of one construction' of my improved lpud speaker,

Fig. 2, a side elevatlon of Fig, il,y a Fig. 3, a cross-section along-line A-B Fig. 7 the arrangement of a sound guid` ing devicefin front view-and.

,Fig.8a vertlcal cross-sectlon through a loud-speaking telephone the diaphragm ofv which is enclosed at one side by a sounddamping chamber, while at its other side it is provided with a sound funnel. Similar parts are indicated by thesame reference characters, in all figures` Referring to Figs. 1-3, it will be seen tha the diaphragm a constructed in. the formof a-straight strip of aluminum is transversely grooved or corrugated and clamped at each end with a certain light preliminary tension-between an insulating piece b anda contact piece c. .An adjusting, screw dabutting withits point against a washer e serveshvfor clamping the diaphragm in position.

. 1 0f a ushered bearmerece ..ewhh `the lendsfithedaphragnili;areiirdisposedsa Theelectromagnet 'has' preferably a rectangular yokel with poles m arranged in axial alinement and upon which are mounted coils p traversed by energizing direct current, provided an electromagnet is employed. A permanent magnet may, however, equally well be employed. According to whether the device is used as a loud speaker or a microphone, the speech current is supplied to the diaphragm a or carried .away from it respectively byy means of thecontact pieces 'c lconnected with the line adapted to conduct thesecurrents.' The rib# bon diaphragm is disposed between the poles of the magnet so that its plane stands in line with the. direction of the-magnetic lines'of force, these lines passing acrossthe ribbon. The diaphragm may preferably `.be given a.V li ght` preliminary ltension in thef direction of its length, a suitable device, for this purpose heilig .illustrated in Fig. 4. Referring to this figure it will bevseen that the dia phra'gin a disposed'` between the poles of the magnet passes at `its ends over liat springs mrounded at their ends and which are adapted to be forced outwards by means of screws y thus putting the; diaphragm under tenslon. Thediaphragm andy the .springs are fixed betweenthe abutments t `and the washers u byscrewsY z.

v.Referring to Fig. 5 the diaphragm is shown mountedon a special carrier. On the poles 'm lof the magnet 7e, are mounted the wedge-shaped poleshoes m, and m.. Be-

- carrier w upon which the diaphragm a is tween the pole shoesisjxed the diaphragm attached by means of screws (Z1, d2, preferyably by means of guide grooves. The' carrier. 'w which consists'of the parts lw1 and 102 separated kby the insulating layers 61' and b2 possesses a central recess across'which the f diaphragm a is stretched. The magnet core is preferably furnished with 'an electrically Q insulated break, so that the alternating current can be passed to the diaphragm a by means ofthe conductors lU, and o, across the poles m, the pole shoes m1 and m2 and the carrier parts "fw, and wg. In 'order to 'improve the contact faces of the diaphragm carrier, which make contact'with the .pole shoes, are preferably provided with a well conducting metal covering, which may consist of copper, silver and the like.

The arrangement of the diaphragm uponA a special carrier is applicable for any kind of diaphragm, in particular for such which are stretched in zigzag, as shown in Fig. 6. Referring to this figure, it will be seen that one of the magnet poles' is formed or provided with a pin g upon which is placed a The adjusting' screw d is journaled- 1n a T-shaped piece f, which engages grooves* u1 and .,zt2, .forstretching.ther diaphragm. l c x Av`ribbonand'Pins S'ywh'ich"cnsist'offnom thin disc r. Upon this disc are provided at the 4top and at the bottom the two clamps magnetic material, such as brass with a coating of shellac or enamel in order to insulate the ribbon passed around these pins.

. In order to facilitate the insertion of the ribbon, the pins s and the bore yholes for' difference of 180.

The Figure 7 shows in front view the arrangement of'. vfunnel?shaped sound guides forthe'purpose oflimiting tliewolurne of air taking part in the oscillations of 'the diaphragm.

ln Fig 8 the arrangement of a sounddamping chamber at theother side of the l diaphragm is shown in vertical longitudinal section. y Referring to these figures, it will be seen that the d1aphragm a is arranged-between kthe poles m of an electromagnet k. Upon' the poles are mounted the` coils p.. The space between the edges of the diaphragm and the poles is preferably chosen'smaller than halfr the Width of the diaphragm. The 'dia-v phragm is disposed between bearing 'pieces z', to 7', and is subjected to a light preliminary stretching by means of springs a: consisting of superimposed,leaves, in the manner of carriage springs, fixed by set screws.-

2 and washers' u upon the hearing pieces 3 and z', and adapted to be forced outwards by adjusting screws y. Upon the bearing pieces z', Aand 2'. a funnel-shaped structure h, which may, for instance, consist of aluminium sheetmetal coated with a suitable varnish, is fixed by means of screws passing through bores in 'the edge of the funnel 'L bent off at substantially right angles. At the other side of the diaphragm a casing or cap n is mounted upon the supporting pieces 3,4 by means of screws (l1, which cap is lined with a sound absorbing material, such as felt or the like. The volume of this cap ymay be made adjustable, if desired.

It will.. be understood, that the funnel k maybe attached in any other suitable manner, for instance by'means of special. carriers. Care must be taken, however, that it comes up so closely to the diaphragm, A

that as far as possible theentire oscillation energy of the diaphragm radiating Vfrom that particular side is transmitted to 'and taken up' by the body of air in the funnel without the production of disturbing oscillations."

For loud-speaking telephones, which .should be eiiective towards both sides on each of the two sides of the diaphragm a funnel should referably be. provided as sound guide. n casel interferences are to be anticipated funnels the dimensions oi which differ from each other are chosen..

It will be understood that I do not limit myself to the exact'details of the constructions described and show n by way of example, but that modifications rwithin the scope of the claims will suggest themselves to persons skilled in the art, without departing from the-spirit of my invention or sacriicing any of its advantages.

What I claim as m invention and desire to secure by Letters atent is -1..In an acoustic device for converting electrical energy into sound energy or sound energy into electrical energy, a light ribbonshaped conductive diaphragm, dlsposed between the poles of -a constant field magnet and adapted to carry'alternating speaking currents, said diaphragm having means for rendering it elastic to enable it to perform motions transversely to its plane of approximately equal `amplitude over its entire length.l l,

2. In an acoustic device for converting electrical `energy into sound energy or sound energy into electrical energy, alight ribbonshaped conductive diaphragm, disposedbe tween the poles of a constant iield magnet an'dadapted to carry alternating speaking currents, said diaphragm having means for i rendering it elasticto enable' it to perform motions transversely to its plane of approximately equal amplitude over its entire length, and means for maintaining'said diaphragm under slight tension.

3. In an acoustic device Afor converting electrical energy into .sound energy or sound energy into electrical energy, a light ribbonshaped conduct-ive diaphragm, dlsposed between the polesof a constant field magnet and adapted to lgairy alternating speaking tween the poles of a constant field magnet and adapted 'to carry alternating speaking currents, said diaphragm having 'transverse 4corrl'igations for renderingit clasticto enable it to perforgn motions transversely to 4its plane of approximately equal amplitude over its entire length, and means for main'- taining said diaphragm under slight tension.

5. In an lacoustic devicel for converting electrical energy into sound energy or sound energy into electrical energy, a ribbonshaped conduct-ive diaphragm disposed between the poles ofa constant field magnet and adapted to carryv alternating currents, said diaphragm being of a weight substan-v tially equal to the weight of the volume 01"; 'air between which volume and the diaphragin the energy exchange occurs, said diaphragm lhaving transverse corrugationsand means for maintaining it at slight tension to Venable 1t to perform motions transversely to its plane of approximately equal amplitude over its entire length.

6. In an acoustic device for converting electrical energy into sound energy or sound energy into electrical energy, a .ribbonshaped diaphragm consisting of aluminum foil not substantially exceeding one-hun-l -dredth of a millimeter in thickness and'being provided withtransverse corrugations, said diaphragm being disposed between the poles of a constant field magnet and adapted to carry alternating currents andmeans for maintaining said diaphragm under slight l tension to enable it to 4perform large motions transversely to its plane of approximately equal amplitude over its ent-ire length.`

-In Atestimony whereof I aix mysignature.

- ERWIN GERLACH. 

